Homework Help:
Momentum Problem on a chain

1. The problem statement, all variables and given/known data
A chain of length L and total mass M is released from rest with its lower end just touching the top of a table. Find the force exerted by the table on the chain after the chain has fallen through a distance x. (Assume each link comes to rest the instant it reaches the table.)

2. Relevant equations
p= mv
ek= (1/2)mv^2

3. The attempt at a solution
First, I tried to find the force by taking the derivative of kinetic energy:
ek= (1/2)mv^2
m= M(L-x)/L, v^2= 2xg
ek= Mxg(L-x)/L
d/dt(ek)= Mgv-2Mgxv/L

F= [d/dt(ek)]/v= Mg-2Mgx/L
But this turns out to be the wrong answer. Any advice? Thanks.1. The problem statement, all variables and given/known data